Transportation refrigeration units are utilized in the transport of perishable goods, with the temperature and environmental controls being critical to the arrival of the perishable goods without damage or spoilage. Typical transportation refrigeration units have sensors within the units to provide data back to a central processing location so that temperature and/or humidity as well as the operating condition of refrigeration units during transportation can be monitored.
Typically units such as Thermo King and the like provide an RS-232 bus. However, for each of the transportation refrigeration units there are multiple sensors that can be activated or provided to sense various conditions depending on the load. Moreover, with varying load requirements come varying requirements for the refrigeration unit itself including requirements not only for the refrigeration unit but also for the electrical generator which powers the unit.
Thus, there has been a problem with the use of only the RS-232 bus to be able to provide adaptability to different loads, to be able to set sensors to different parameter levels and to be able to activate certain sensors as well as to provide control of the sensors that are activated.
In the case of transportation refrigeration units, the sensors are those associated with food products. The sensors could be spoilage sensors, sensors to determine changes in temperature, and additional sensors inside the transportation refrigeration unit to monitor temperature at different places, since temperature is not necessarily uniform throughout a unit. Note, there is oftentimes a requirement to be able to add additional sensors to a single temperature sensor and there is a requirement to be able to add the sensors and control the sensors remotely.
Present transportation refrigeration units today pass data through the traditional RS-232 interface. However, the RS-232 interface does not support multiport direct communications with the sensor system to permit listening in directly to each of the sensors and to query selected sensors.
Also with sensors, there is a necessity to provide a control bus because it is important to be able to control the signal-to-noise ratio. This is done by adjusting sensor parameters and an RS-232 data bus does not have a signal-to-noise control capability.